What Tierra and Avida so eloquently appreciate is the idea that evolution emerges as a property of reproducing organisms under the pressure of natural selection. That is to say, there is not an all-encompassing algorithm being applied to biological organisms, rather evolution emerges the organisms themselves. Current approaches in evolutionary computation do not reflect the emergence of evolution, and rather embody the idea that evolution is applied to a population algorithmically. Self-reproduction is vital for the evolution of digital organisms, as without it, selection must be hand-designed and performed by the simulator; hence, evolutionary algorithms and evolutionary self-replicators are distinguished by a matter of natural selection versus artificial selection [1]}, [2]}.
